1. Field of the Invention
The present invention relates to an optical disc system suitable for use with a so-called Sony Mini Disc (hereinafter referred to as an MD) system, for example.
2. Description of the Related Art
MDs that are now available on the market are generally classified as, for example, an MD from which recorded music can be reproduced only in use (hereinafter referred to as a pre-mastered MD when necessary) and an MD on which the user can freely record desired information (hereinafter referred to as a recordable MD when necessary).
The recordable MD according to the Sony Mini Disc format has one frame formed of 24 bytes and one sector formed of 98 frames. In this case, an interleaving length of a CIRC (Cross Interleave Reed-Solomon Code) as an error correction code is 108 frames, which is longer than one sector. Therefore, when data is recorded on the recordable MD, 3 sectors between adjacent data recording areas must be used as "useless sectors". The area of the "useless sector" area is called a link area. In other words, if 108 frames were not prepared before and after data were recorded respectively, then the interleaving would not be completed. For this reason, the link area of 3 sectors must be provided between the adjacent data recording areas.
If data is recorded on the recordable MD from any position, then the link areas are scattered on many portions of the recordable MD, thereby deteriorating a utilization factor of the recordable MD. For this reason, data is recorded on the recordable MD at recording units of a certain large data amount. In the recordable MD, this recording unit is called a cluster and one cluster is formed of 36 sectors. In one cluster, the leading 3 sectors are assigned to sectors of the above link area (leading 3 sectors will hereinafter be referred to as link sectors), and the next 1 sector is assigned to sector for sub data which is added data (this sector will hereinafter be referred to as a sub data sector. The remaining 32 sectors are assigned to data recording sectors.
FIG. 1 shows a data format of about one cluster of the recordable MD thus described. As shown in FIG. 1, 1 cluster includes a link area having link sectors LS formed of 3 sectors, a sub data sector SS formed of one sector and a data area formed of data sectors DS formed of 32 sectors.
In the pre-mastered MD, all data are written by one access and 3 sectors of the link area are not necessary. Therefore, the 4 leading sectors are all assigned to the sub data sector SS. On the sub data sector SS are recorded graphic data, text data of a recorded musical accompaniment for amateur singers (so-called KARAOKE) and so on. Thus, it is used for KARAOKE and so on.
The inventor of the present application has an idea that the recordable MD can be used as a mass storage in and from which general data can be recorded and reproduced.
Reproducible CD-ROMs are generally used as mass storage of general data.
A format of the CD-ROM will be described below. One frame thereof is formed of 24 bytes, and 1 sector is formed of 98 frames. A disc is rotated in a CLV (constant linear velocity) fashion and its linear velocity is 1.2 to 1.4 m/s, which is the same as the existing MD system.
Therefore, it is considered that, if data on the CD-ROM were transferred to the recordable MD of the MD system and the data thus transferred to the recordable MD were transferred from the MD system to the hardware which reproduces the CD-ROM, then the transferred data could be processed as though the CD-ROM were directly played back by the above hardware.
However, since all data are recorded on the CD-ROM by a stamper in one process, the link area of 3 sectors need not be provided. Further, the sub data sector of 1 sector also is not provided. There is then the problem that a substantial data transfer rate of the MD system is lowered to 8/9 (=(36-4)/36) as compared with 150 kB/s of the maximum average data transfer rate of the CD-ROM. Therefore, the MD system cannot be applied to the existing software/hardware system that was produced on the basis of the data transfer rate of the CD-ROM, such as a moving picture made by the MPEG (moving picture image coding experts group) or the like.